NinJump Deluxe HD is the souped-up version of the free, popular NinJump, an infinitely scrolling vertical-climbing game with a super-simple one-tap interface.
As with other games in this genre (whether vertically or horizontally oriented), the goal is to get as far as you can without dying. You play an ultranimble ninja, jumping between two walls on the left and right of the screen to avoid obstacles and enemies. You're always moving up--quickly!--and you tap anywhere on the screen to leap between the two walls. In the game's classic version, you scale generically pagoda-like structures and fight ninja-esque enemies (other ninjas with throwing stars, and even some ninja birds and squirrels, which you have to attack at just the right angle). If you defeat three of the same kind of enemy in a row--like three rockets or three throwing stars--you get to shoot ahead invincibly for a few seconds to rack up some free points. The Deluxe version of the game adds three new levels, in addition to Classic: Castle, Pirates, and Jungle, each with the same core mechanic but with new and suitably themed enemies.
NinJump Deluxe HD has a little more replay value than the original (trying to top your scores, then sharing them on GameCenter and elsewhere, is always fun), but neither game has very much depth. Still, addictive pick-up-and-play games like this are all about execution--from the music to the graphics to the simplicity of the gameplay--and NinJump Deluxe HD gets all the details right.